Are you asking what the most destructive habit is? I think the second-most destructive habit is any habit that subjects you to addiction. I know that drugs can destroy your life, moving from addiction to prostitution to death.
I also know that there are people who can use drugs in a way that it helps them to reduce pain. Since we all have bad habits (even if you believe you are a saint), the worst habit is to be selfish. That does not mean you have to give money to poor people who are begging (and might be selfish as hell themselves).
If everyone would think everything is about 'winning' or 'money', then you start to lose the deep contact with your environment and finally with yourself. Because you are your environment; and if you have a drug addiction and have a negative selfish orientation, then you will never get out of the old patron. Help others will help you.
I write & speak about personal development
Not constantly improving yourself.
Without learning & self-improvent your life will stay put. You stay average, ordinary. There's nothing new and exciting.
Okay, we can talk about smoking and drinking and so one, but we all know that those are dangerous. But so many people don't think about their knowledge. Or lack of it.
Ezra Hananiah Jalin
Born - again Christian, former Atheist, Filmmaker, Writer, Christian Apologists.
The habit that destroys not only your mindset, but also your wellbeing. The habit that seeks pleasure and shortcuts without hard labour. The habit that seeks to complete tasks without struggle. The habit that makes you worse day by day. The habit that corrupts the system that revolves around human: Labour and Excellence. The habit that does not produces great fruit and discourage harvests. The habit that seeks to procrastinate on details.
If your habit contains such, get rid of it immediately.
A doctor-to be
In no specific order:
Not being faithful to yourself.
Saying everybody "Yes" in order to socially accommodate yourself.
Not prioritizing about your life and your work ( Procrastinating )